Standard package CMOS based MMIC (Microwave Monolithic integrated Circuits) devices are for cost reasons widely used in microwave frequency applications. MMIC amplifiers typically consist of arrays of transistors coupled in parallel.
Since MMIC amplifiers typically have a fixed upper power limit, a distribution net or coupling network is needed in applications where the power output exceeds the output power of available individual MMICs.
Distributing networks are widely used in antenna array designs. One such example is given in prior art document US2001/0054983 (FIG. 1) showing an amplifier/antenna device comprising three stages of parallel-coupled MMIC CMOS FET amplifier elements, for distributing power across multiple antenna elements of an antenna array.
In antenna/amplifiers devices of the above kind it is possible to distribute a signal on the input terminal to the various output terminals with the same phase delay. One drawback of the above arrangement is that the circuit is sensitive for manufacturing tolerances, with breaches leading to signal reflections and power losses. From a practical perspective, it would therefore be necessary to provide a plurality of tuning elements to accomplish stable performance over a wide frequency bandwidth.
For similar circuits as shown above, the branching network coupled to MMIC amplifiers may be designed so that the output impedance of the branching network corresponds to the input impedance of the MMIC amplifier. Moreover, typically the input impedance at the input terminal is typically rendered close to the commonly chosen system input impedance value of 50Ω in order to provide connectivity with other equipment for avoiding reflections.
US2002/0036541 shows a MMIC power amplifier comprising a 2-4-8-topology power splitter network and combining network for evenly splitting the power to the MMIC's and for combing the output power. The drain of a preceding stage is coupled to the gates of a proceeding stage via a matching and splitting network. The amplifier seems to constitute a narrow bandwidth solution.
The article “1 Watt 17.7 GHz-32 GHz Linear Power Amplifier, application note #52—Rev. A. 1, July 1998”, Agilent Technologies, shows a thin film microcircuit network based on a variation of a Wilkinson divider, which divides the power to a plurality of MMIC amplifier devices and combines the respective outputs. The network maintains a 50 Ohm impedance at the input and output terminals.